Cataracts and macular degeneration are widely thought to result from photochemical damage to the intraocular lens and retina, respectively. Blue light exposure has also been shown to accelerate proliferation of uveal melanoma cells. The most energetic photons in the visible spectrum have wavelengths between 380 and 500 nm and are perceived as violet or blue. The wavelength dependence of phototoxicity summed over all mechanisms is often represented as an action spectrum, such as is described in Mainster and Sparrow, “How Much Blue Light Should an IOL Transmit?” Br. J. Opthalmol., 2003, v. 87, pp. 1523-29 and FIG. 6. In eyes without an intraocular lens (aphakic eyes), light with wavelengths shorter than 400 nm can cause damage. In phakic eyes, this light is absorbed by the intraocular lens and therefore does not contribute to retinal phototoxicity, however it can cause optical degradation of the lens or cataracts.
The pupil of the eye responds to the photopic retinal illuminance, in trolands, which is the product of the incident flux with the wavelength-dependent sensitivity of the retina and the projected area of the pupil. This sensitivity is described in Wyszecki and Stiles, Color Science: Concepts and Methods Quantitative Data and Formulae (Wiley: N.Y.) 1982, esp. pages 102-107.
Current research indicates that over the course of one's life, beginning with that of an infant, metabolic waste byproducts accumulate within the pigment epithelium layer of the retina, due to light interactions with the retina. This metabolic waste product is characterized by certain fluorophores; one of the most prominent being lipofuscin constituent A2E. It has been shown that this particular fluorophore is excited most significantly by blue light radiation of the wavelength of about 430 nanometers. It is theorized that a tipping point is reached when a combination of a build-up of this metabolic waste (specifically the lipofuscin fluorophore) has achieved a certain level of accumulation, the human body's physiological ability to metabolize within the retina certain of this waste has diminished as one reaches a certain age threshold, and a blue light stimulus of the proper wavelength causes drusen to be formed. It is believed that the drusen then further interfere with the normal physiology/metabolic activity which allows for the proper nutrients to get to the photoreceptors thus contributing to AMD (age related macular degeneration). AMD is believed to be the leading cause of blindness in the elderly.
From a theoretical perspective, the following appears to take place:                1) Waste buildup occurs within the pigment epithelial level starting from infancy through out life.        2) Retinal metabolic activity and ability to deal with this waste typically diminish with age.        3) The macula pigment typically decreases as one ages, thus filtering out less blue light.        4) Blue light causes the lipofuscin to become toxic.        5) The resulting toxicity damages pigment epithelial cells.        
It has been shown that if about 50% of the blue light within the wavelength range of 430±30 nm is blocked, cell death caused by the blue light may be reduced by up to 80%. External eyewear such as sunglasses, spectacles, goggles, and contact lenses that block blue light in an attempt to improve eye health are disclosed, for example, in U.S. Pat. No. 6,955,430 to Pratt. Other ophthalmic devices whose object is to protect the retina from this phototoxic light include intraocular and contact lenses. These ophthalmic devices are positioned in the optical path between environmental light and the retina and generally contain or are coated with dyes that selectively absorb blue and violet light.
Other lenses are known that attempt to decrease chromatic aberration by blocking blue light. Chromatic aberration is caused by optical dispersion of ocular media including the cornea, intraocular lens, aqueous humour, and vitreous humour. This dispersion focuses blue light at a different image plane than light at longer wavelengths, leading to defocus of the full color image. Conventional blue blocking lenses are described in U.S. Pat. No. 6,158,862 to Patel et al., U.S. Pat. No. 5,662,707 to Jinkerson, U.S. Pat. No. 5,400,175 to Johansen, and U.S. Pat. No. 4,878,748 to Johansen.
Conventional methods for reducing blue light exposure of ocular media typically completely occlude light below a threshold wavelength, while also reducing light exposure at longer wavelengths. For example, the lenses described in U.S. Pat. No. 6,955,430 to Pratt transmit less than 40% of the incident light at wavelengths as long as 650 nm, as shown in FIG. 6 of Pratt '430. The blue-light blocking lens disclosed by Johansen and Diffendaffer in U.S. Pat. No. 5,400,175 similarly attenuates light by more than 60% throughout the visible spectrum, as illustrated in FIG. 3 of the '175 patent.
Balancing the range and amount of blocked blue light may be difficult, as blocking and/or inhibiting blue light affects color balance, color vision if one looks through the optical device, and the color in which the optical device is perceived. For example, shooting glasses appear bright yellow and block blue light. The shooting glasses often cause certain colors to become more apparent when one is looking into a blue sky, allowing for the shooter to see the object being targeted sooner and more accurately. While this works well for shooting glasses, it would be unacceptable for many ophthalmic applications.
It has been found that conventional blue-blocking reduces visible transmission, which in turn stimulates dilation of the pupil. Dilation of the pupil increases the flux of light to the internal eye structures including the intraocular lens and retina. Since the radiant flux to these structures increases as the square of the pupil diameter, a lens that blocks half of the blue light but, with reduced visible transmission, relaxes the pupil from 2 mm to 3 mm diameter, will actually increase the dose of blue photons to the retina by 12.5%. Protection of the retina from phototoxic light depends on the amount of this light that impinges on the retina, which depends on the transmission properties of the ocular media and also on the dynamic aperture of the pupil. Previous work to date has been silent on the contribution of the pupil to prophylaxis of phototoxic blue light.
Another problem with conventional blue-blocking is that it can degrade night vision. Blue light is more important for low-light level or scotopic vision than for bright light or photopic vision, a result which is expressed quantitatively in the luminous sensitivity spectra for scotopic and photopic vision. Photochemical and oxidative reactions cause the absorption of 400 to 450 nm light by intraocular lens tissue to increase naturally with age. Although the number of rod photoreceptors on the retina that are responsible for low-light vision also decreases with age, the increased absorption by the intraocular lens is important to degrading night vision. For example, scotopic visual sensitivity is reduced by 33% in a 53 year-old intraocular lens and 75% in a 75 year-old lens. The tension between retinal protection and scotopic sensitivity is further described in Mainster and Sparrow, “How Much Light Should and IOL Transmit?”, Br. J. Opthalmol., 2003, v. 87, pp. 1523-29.
Conventional approaches to blue blocking also may include cutoff or high-pass filters to reduce the transmission below a specified blue or violet wavelength to zero. For example, all light below a threshold wavelength may be blocked completely or almost completely. For example, U.S. Pub. Patent Application No. 2005/0243272 to Mainster and Mainster, “Intraocular Lenses Should Block UV Radiation and Violet but not Blue Light,” Arch. Ophthal., v. 123, p. 550 (2005) describe the blocking of all light below a threshold wavelength between 400 and 450 nm. Such blocking may be undesirable, since as the edge of the long-pass filter is shifted to longer wavelengths, dilation of the pupil acts to increase the total flux. As previously described, this can degrade scotopic sensitivity and increase color distortion.